Investigation on Resonance Self-Shielding Calculation for PWR Cladding Materials Based on Equivalence Theory

The treatment of resonance self-shielding effect is one of the key factors for reactivity accuracy in PWR lattice code. The PWR cladding materials for zirconium isotopes also has the resonance self-shielding effect. Ignoring the influence of resonance self-shielding effect for cladding materials, it can cause 100~300 pcm errors in reactivity predictions. Now, the reference dilution cross section and cladding equivalence theory can be used in treating the resonance self-shielding effect for cladding material, but the applicability and accuracy of these methods has not been completely tested. Therefore, a series of PWR cases are used in testing the applicability of these methods computed by DRAGON code. The main impact factors for the resonance self-shielding effect in cladding material and the applicability of these two methods are determined. The results show that the resonance self-shielding effect in cladding material is only related to nuclide density, thickness and water/uranium ratio in the moderator region. The reference dilution cross section satisfies the typical PWR cases, however it can cause more errors in the great change of the above three factors. The new equivalence theory is more accurate and flexible, which can be used in different PWR cladding materials for the calculation of the resonance self-shielding effect.